Influence of Fluid Compressibility and Movements of the Swash Plate Axis of Rotation on the Volumetric Efficiency of Axial Piston Pumps

This paper describes the design of a swash plate axial piston pump and the theoretical models describing the bulk modulus of aerated and non-aerated fluids. The dead space volume is defined and the influence of this volume and the fluid compressibility on the volumetric efficiency of the pump is considered. A displacement of the swash plate rotation axis is proposed to reduce the dead space volume for small swash plate swing angles. A prototype design of a pump with a displaced axis of rotation of a swash plate with two directions of delivery is presented, in which the capacity is changed by means of a valve follow-up mechanism. Comparative results for a pump with a displaced and a non-displaced swash plate rotation axis are presented, which confirm that displacement of the swash plate rotation axis causes an increase in volumetric efficiency that is apparent for high pressure discharge and small swash plate angles. The determined characteristics were compared with a mathematical model taking into account the compressibility of the fluid in the dead space volume and a satisfactory consistency was obtained.

Presample Volume Necessary to Obtain Accurate Laboratory Parameters from Central Venous Catheters in Dogs

ABSTRACT We compared laboratory parameters from central venous catheters using multiple presample volumes (PSVs) to venipuncture values. Blood was obtained from dogs for a venous blood gas, packed red blood cell volume (PCV), total solids (TS), and a coagulation panel. Blood was drawn both by venipuncture and from the catheter (using PSVs 300%, 600%, and 1200% of the dead space volume). Twenty dogs were enrolled. Venipuncture values were significantly higher than those obtained from the catheter for PCV (300% [P = .007], 600% [P = .005], and 1200% [P = .02]), TS (300% [P = .006] and 600% [P = .04]), and lactate (600% [P = .04] and 1200% [P = .01]). Venipuncture values were significantly lower than those obtained from a catheter for pH (1200% [P = .008]) and chloride (300% [P = .04], 600% [P = .003], and 1200% [P = .03]). An increase was found in prothrombin time in samples drawn with 600% PSV compared with 1200% (P = .008). The PCV and TS are diluted when smaller PSVs are used. A 1200% PSV best approximated the PCV and TS obtained by venipuncture. A 300% PSV may be adequate to evaluate coagulation and venous blood gas values.

The Mostafa Maged four-stitch technique to avoid leaving dead space during repairing the episiotomy

Most women who are primigravida are mostly confronted with episiotomy during child-birth to prevent the perineal and vaginal lacerations which could be performed at birth. There are many types of episiotomies which are median, mediolateral and J-shaped episiotomy. In here, we performed the mediolateral suture due to its safety. All episiotomy were taken by the Mostafa Maged four-stitch technique. Prevention of the formation of the dead space during the repair of episiotomy so avoiding hematoma formation in the episiotomy area after child-birth. It is an Interventional study. The Mostafa Maged four-stitch technique uses the absorbable vicryls treads with round needles 75 mm. the results of this new technique are Prevention of the dead space formation, Good and tight hemostasis of the episiotomy is achieved, strong approximation of the two edges of the episiotomy, cosmetically, it is so good. The invention of this new technique (Mostafa Maged technique) has shown its effectiveness in those fifteen patients in preventing the dead space during suturing the episiotomy in primigravida cases.

Modified Canal Wall Down Mastoidectomy Without Meatoplasty

It is important to decide which procedure to employ between canal wall up mastoidectomy and canal wall down mastoidectomy (CWDM) as each procedure has its own advantages and disadvantages. To combine the advantages and compensate the disadvantages of each procedure, various methods and approaches have been devised. Mastoid and epitympanic obliteration, which minimizes the dead space in the mastoid cavity, was previously known to prevent the occurrence of retraction pockets. We performed mastoid and epitympanic obliteration also to prevent the occurrence of cavity problems without meatoplasty. Here we describe the surgical procedures for modified CWDM without meatoplasty and mastoid obliteration using autologous materials.

Dead space ratio as a tool in nitric oxide weaning: a study in pulmonary hypertensive disease

Objectives: To describe the association between successful weaning of inhaled nitric oxide and trends in dead space ratio during such weans in patients empirically initiated on nitric oxide therapy out of concern of pulmonary hypertensive crisis. Patients: Children in a cardiac intensive care unit initiated on inhaled nitric oxide out of clinical concern for pulmonary hypertensive crisis retrospectively over 2 years. Measurements and Main Results: Twenty-seven patients were included, and nitric oxide was successfully discontinued in 23/27. These patients exhibited decreases in dead space ratio (0.18 versus 0.11, p = 0.047) during nitric oxide weaning, and with no changes in dead space ratio between pre- and post-nitric oxide initiation (p = 0.88) and discontinuation (p = 0.63) phases. These successful patients had a median age of 10 months [4.0, 57.0] and had a pre-existent diagnosis of CHD in 6/23 and pulmonary hypertension in 2/23. Those who failed nitric oxide discontinuation trended with a higher dead space ratio at presentation (0.24 versus 0.10), were more likely to carry a prior diagnosis of pulmonary hypertension (50% versus 8.7%), and had longer mechanical ventilation days (5 versus 12). Conclusions: Patients empirically placed on nitric oxide out of concern of pulmonary hypertensive crisis and successfully weaned off showed unchanged or decreased dead space ratio throughout the initiation to discontinuation phases of nitric oxide therapy. Trends in dead space ratio may aid in determining true need for nitric oxide and facilitate effective weaning. Further studies are needed to directly compare trends between success and failure groups.

The Association Between Ventilatory Ratio and Mortality of Adult Patients with ARDS: Systematic Review and Meta-Analysis

Background: Ventilatory ratio is a simple bedside index of impaired efficiency of ventilation and correlates well with physiological dead space fraction in patients with ARDS. So it was regarded as a dead-space marker associated with mortality in mechanically ventilated adults with ARDS. However, the association between VR and outcome of patients with ARDS remains largely unknown. Methods: We searched articles in three electronic databases including PubMed, EMBASE and Web of Science. All the English publications up to 1 st Oct. 2021 will be searched without any restriction of countries. All the observational study that investigated the association between ventilatory ratio and the mortality of ARDS patients were identified in this meta-analysis. The main outcome was mortality. Summary estimates of effect using odds ratio (OR) for dichotomous outcomes with accompanying 95% confidence interval (CI) were expressed. Results: A total of 9 trials enrolling 5638 patients were finally included in this meta-analysis. The results revealed that the use of ventilatory ratio could be significantly related to the mortality in adult ARDS (OR=1.27; 95% CI 1.10 to 1.47; P=0.001). Ventilatory ratio may have the capability of predicting the mortality of NON- COVID-related patients (OR 1.39, 95% CI 1.12 to 1.73 P = 0.003) while it has no predictable significance in patients with COVID (OR 1.18, 95% CI 0.94 to 1.48 P = 0.16). Importantly, the dynamic changes of VR adds more predictable value (OR 1.21 vs 1.19). Conclusion: Our study suggests that ventilatory ratio can be regarded as a valuable marker to predict the mortality of adult patients with ARDS. Compared to patients with COVID, ventilatory ratio is more predictable in patients with NON-COVID. What’s more, the dynamic changes of VR may have the potential to improve the prognostic value.

Positive end-expiratory pressure in COVID-19 acute respiratory distress syndrome: the heterogeneous effects

Background We hypothesized that as CARDS may present different pathophysiological features than classic ARDS, the application of high levels of end-expiratory pressure is questionable. Our first aim was to investigate the effects of 5–15 cmH2O of PEEP on partitioned respiratory mechanics, gas exchange and dead space; secondly, we investigated whether respiratory system compliance and severity of hypoxemia could affect the response to PEEP on partitioned respiratory mechanics, gas exchange and dead space, dividing the population according to the median value of respiratory system compliance and oxygenation. Thirdly, we explored the effects of an additional PEEP selected according to the Empirical PEEP-FiO2 table of the EPVent-2 study on partitioned respiratory mechanics and gas exchange in a subgroup of patients. Methods Sixty-one paralyzed mechanically ventilated patients with a confirmed diagnosis of SARS-CoV-2 were enrolled (age 60 [54–67] years, PaO2/FiO2 113 [79–158] mmHg and PEEP 10 [10–10] cmH2O). Keeping constant tidal volume, respiratory rate and oxygen fraction, two PEEP levels (5 and 15 cmH2O) were selected. In a subgroup of patients an additional PEEP level was applied according to an Empirical PEEP-FiO2 table (empirical PEEP). At each PEEP level gas exchange, partitioned lung mechanics and hemodynamic were collected. Results At 15 cmH2O of PEEP the lung elastance, lung stress and mechanical power were higher compared to 5 cmH2O. The PaO2/FiO2, arterial carbon dioxide and ventilatory ratio increased at 15 cmH2O of PEEP. The arterial–venous oxygen difference and central venous saturation were higher at 15 cmH2O of PEEP. Both the mechanics and gas exchange variables significantly increased although with high heterogeneity. By increasing the PEEP from 5 to 15 cmH2O, the changes in partitioned respiratory mechanics and mechanical power were not related to hypoxemia or respiratory compliance. The empirical PEEP was 18 ± 1 cmH2O. The empirical PEEP significantly increased the PaO2/FiO2 but also driving pressure, lung elastance, lung stress and mechanical power compared to 15 cmH2O of PEEP. Conclusions In COVID-19 ARDS during the early phase the effects of raising PEEP are highly variable and cannot easily be predicted by respiratory system characteristics, because of the heterogeneity of the disease.

Computations of State Ventilation and Respiratory Parameters

Background: In mechanical ventilation, there are still some challenges to turn a modern ventilator into a fully reactive device, such as lack of a comprehensive target variable and the unbridged gap between input parameters and output results. This paper aims to present a state ventilation which can provide a measure of two primary, but heterogenous, ventilation support goals. The paper also tries to develop a method to compute, rather than estimate, respiratory parameters to obtain the underlying causal information. Methods: This paper presents a state ventilation, which is calculated based on minute ventilation and blood gas partial pressures, to evaluate the efficacy of ventilation support and indicate disease progression. Through mathematical analysis, formulae are derived to compute dead space volume/ventilation, alveolar ventilation, and CO2 production. Results: Measurements from a reported clinical study are used to verify the analysis and demonstrate the application of derived formulae. The state ventilation gives the expected trend to show patient status, and the calculated mean values of dead space volume, alveolar ventilation, and CO2 production are 158mL, 8.8L/m, and 0.45L/m respectively for a group of patients. Discussions and Conclusions: State ventilation can be used as a target variable since it reflects patient respiratory effort and gas exchange. The derived formulas provide a means to accurately and continuously compute respiratory parameters using routinely available measurements to characterize the impact of different contributing factors.